The present invention relates to methods and apparatus for dispensing a fluid and more particularly to methods and apparatus for depositing solid carbon dioxide in a predetermined pattern.
Carbon dioxide has been used for many years as a refrigerant for items of food and other material. Typically, liquid carbon dioxide is maintained under a pressure above the triple point pressure (60 psig) and is released through a nozzle to atmospheric pressures which results in a conversion of liquid carbon dioxide to the solid and gaseous phases. This phase conversion results in a reduction in the temperature of carbon dioxide to approximately -109.degree. F. Typically, liquid CO.sub.2 is used to supply the refrigeration necessary to either freeze or chill items such as food or the like in tunnel freezers, spiral belt freezers, tumblers, blenders, etc. It is common practice to simply discharge liquid CO.sub.2 through a nozzle into one of the aforementioned refrigerating devices to reduce the temperature therein and products passed therethrough to predetermined values. The use of nozzles, however, results in a point source discharge of a spray of solid and gaseous carbon dioxide and consequently, the resulting flow of particles of solid CO.sub.2, i.e. snow, is not readily controllable. In many installations, liquid CO.sub.2 may be injected into a freezing tunnel and simply blown by fans to sublime solid CO.sub.2 which in turn chills the internal atmosphere of the freezing or refrigerating device. A typical device is illustrated in U.S. Pat. No. 3,708,995 which, as mentioned above, operates to simply move CO.sub.2 about the interior of the freezing tunnel.
Another technique for depositing carbon dioxide snow on products to be refrigerated is illustrated in U.S. Pat. No. 3,757,367. In the devices illustrated in these references, liquid CO.sub.2 is discharged through a nozzle into a J-tube configuration wherein a stream of solid and gaseous CO.sub.2 is directed downwardly and then caused to flow upwardly toward an outlet of the tube. Prior to reaching the outlet, a separator blade or other sharp protruberance is utilized to separate the solid and gaseous CO.sub.2 such that the separated solid CO.sub.2 is removed from the tube and is caused to fall downwardly in a random fashion onto product being refrigerated. U.S. Pat. No. 4,111,671 discloses a similar device utilizing a separator blade although the solid-gaseous carbon dioxide stream is not supplied to an upwardly extending portion of the conduit into which liquid CO.sub.2 is supplied. It has been found that the devices illustrated in these references rely on the flow of solid CO.sub.2 through a relatively small orifice at the point of solid-gas separation. Consequently, solid CO.sub.2 tends to agglomerate at such a point and eventually can clog the orifice which frustrates the intended purpose of this device. In order to avoid such clogging, it is known to heat the separating blade or other protruberance, although this technique requires that CO.sub.2 be dispensed on an intermittent, as opposed to continuous, basis. Thus, the separation devices described in these references have not been found to be fully effective from an operational viewpoint and at best, simply dispense solid carbon dioxide in a random fashion on a product being refrigerated and does not enable the deposition of a controlled, predetermined pattern of carbon dioxide snow on a moving surface.
U.S. Pat. No. 4,166,364 describes a technique which ostensibly ameliorates the problems of blade separation employed in J-tube solid-gas CO.sub.2 separating devices. In the device described in this patent, a hood arrangement is utilized to deflect solid CO.sub.2 emanating from a J-tube downwardly onto a product to be refrigerated. Although this technique may improve solid-gaseous CO.sub.2 separation, the device is bulky and not readily adapted for use with tunnel freezers. Furthermore, this device does not permit the formation of ribbons of solid carbon dioxide of a substantially controlled, uniform thickness on a moving surface.
In the course of refrigerating products such as hamburger patties on a conveyor belt of a tunnel freezer, it has been found that the top side of such patties is readily frozen upon contact with the chilled ambient atmosphere in the tunnel freezer. However, the underside of such patties is not so easily refrigerated or frozen even though the patties are conveyed on a wire link belt or the like. Thus, in order to reduce the residence time of patties in the tunnel and hence reduce the consumption of CO.sub.2 refrigerant required per unit weight of patties frozen, it is beneficial to deposit a layer of solid refrigerant on the belt of a tunnel freezer or other surface supporting the items being refrigerated. Upon exposure of such items to the internal atmosphere of the refrigerating device, heat is effectively removed from the items from both the top and bottom surfaces upon entry into the refrigerating device. Prior art refrigerating devices, as mentioned above, have not been adequate to so refrigerate both sides of an item and devices for depositing carbon dioxide snow onto products being refrigerated have not been effective to deposit CO.sub.2 snow on conveyor belts or the like in predetermined patterns of controlled width and uniform thickness. Thus, a clear need exists in the art for a device and method for effectively depositing ribbons of solid carbon dioxide in predetermined patterns of uniform thickness.